1. Field of the Invention
The present invention relates to a plunger-type liquid delivery pump for delivering liquid by sliding the tip end of a plunger inside a pump chamber provided in a pump head and repeating suction of liquid from a suction port and discharge of the liquid from a discharge port.
2. Description of the Related Art
A plunger-type liquid delivery pump slides a tip end portion of a plunger inside a pump chamber by mounting a pump head including the pump chamber inside to a tip end portion of a pump body and by causing a crosshead holding a base end of the plunger to reciprocate in the axial direction of the plunger inside the pump body.
The pump head is provided with an inlet channel for allowing liquid to flow into the pump chamber and an outlet channel for allowing the liquid to flow out of the pump chamber, A check valve is provided to each of the inlet channel and the outlet channel. According to such a structure, when the plunger is driven in the direction of being pulled out from the pump chamber (hereinafter referred to as a suction direction), the pressure inside the pump chamber is reduced, causing the check valve on the inlet channel side to open and the check valve on the outlet channel side to close, and liquid is suctioned into the pump chamber (suction operation). On the other hand, when the plunger is driven in the direction of being pushed into the pump chamber (hereinafter referred to as a discharge direction), the pressure inside the pump chamber is increased, causing the check valve on the inlet channel side to close and the check valve on the outlet channel side to open, and liquid inside the pump chamber is discharged through the outlet channel (discharge operation). Liquid delivery is performed by continuously performing such suction operation and discharge operation.
A plunger seal for preventing liquid leakage from the pump chamber is mounted on the pump head. The plunger seal is, a ring-shaped elastic member having a through hole allowing penetration of the plunger and is for sealing an opening of the pump chamber through which the plunger is inserted while allowing the plunger to slide inside the through hole.
The plunger seal is supported by a tip end surface of the pump body in such a way that the plunger seal is pressed toward the pump chamber side. A hole is provided to the tip end surface of the pump body so as to guide the tip end portion of the plunger to the pump head side. However, when the pressure inside the pump chamber becomes high, there is a problem that the plunger seal is deformed by the pressure, causing a part of the plunger seal to enter between the inner circumferential surface of the hole of the tip end surface of the pump body and the outer circumferential surface of the plunger, and thereby interfering with driving of the plunger and also accelerating deterioration of the plunger seal.
To cope with the problem described above, it is conceivable to reduce the inner diameter of the hole of the tip end surface of the pump body so as to reduce the gap to the plunger. The outer circumferential surface of the plunger is held by the plunger seal mounted on the pump head side, and the plunger reciprocates while sliding on the inner circumferential surface of the plunger seal, and thus, the track of the axis, at the time of operation of the plunger is determined by the positional relationship to the plunger seal. However, due to the assembly tolerance or the like of the pump head and the pump body, the positional relationship between the hole of the tip end surface of the pump body and the plunger seal is not always the same, and there is a problem that, if the inner diameter of the hole of the tip end surface of the pump body is made too small, the inner circumferential surface of the hole contacts the outer circumferential surface of the plunger, and damages to the plunger and the like may occur.
Because of such a problem, a backup ring is generally mounted on the back surface side of the plunger seal of the pump head (see U.S. Pat. No. 9,194,391B2). Since the backup ring is mounted on the pump head side, the positional relationship between a through hole provided to the backup ring and the through hole of the plunger seal is not affected by the assembly tolerance of the pump head and the pump body, and the inner diameter of the through hole of the backup ring may be made smaller than the hole of the tip and surface of the pump body, and deformation of the plunger seal may thereby be suppressed.